Well, like I said, I think putting it directly on the texture would be a huge pain. There's no easy way to access a letter texture, much less a whole word; or put it on only 1 side; or scale/rotate/position the word pixels onto the mainTexture pixels.

If you have a few fixed phrases, most people would just pre-make textures with those, get them all nice, and swap textures (or even materials) in-game.